Liquid crystal displays and organic light emitting displays have been gaining popularity as alternatives to conventional CRTs due to their advantages of small size, light weight, and low power consumption. Currently, these displays are typically mounted in large-sized products, such as monitors and TVs, as well as portable devices, such as mobile phones and personal digital assistants.
FIG. 1 is an exploded perspective view illustrating a conventional portable display device. FIG. 1 shows a dual display device used in mobile phones and the like.
Referring to FIG. 1, the conventional portable display device 60 includes a top chassis 2, a liquid crystal display panel 4, a backlight assembly 50, a bottom chassis 22, a first printed circuit board 24, a second printed circuit board 26, and a light emitting display panel 30.
The liquid crystal display panel 4 displays predetermined images. To display images, the first liquid crystal display panel 4 includes a first substrate 4a, a second substrate 4b, and a liquid crystal layer (not shown) injected between the first substrate 4a and the second substrate 4b. 
The second substrate 4b includes a plurality of thin film transistors (TFTs) arranged in a matrix form (not shown). A source electrode of each TFT is connected to a data line (not shown), and a gate electrode thereof is connected to a scan line (not shown). A drain electrode of each TFT is connected to a pixel electrode (not shown) made of transparent indium tin oxide (ITO) of a conductive material. The TFTs are turned on when the scan line is supplied with a scan signal, and supply a data signal from the data line to the pixel electrode.
An integrated circuit 6 is located on one side of the second substrate 4b, and the data signal and scan signal are supplied from the integrated circuit 6. A protective layer 8 is deposited around the integrated circuit 6.
The first substrate 4a is arranged facing the second substrate 4b. A common electrode made of ITO is deposited on the front surface of the first substrate 4a. The common electrode is applied with a predetermined voltage, and accordingly a predetermined electric field is generated between the common electrode and the pixel electrode. The array angle of the liquid crystal injected between the first substrate 4a and the second substrate 4b varies with the electric field, and the optical transparency also varies according to the variation of the array angle, to thereby display desired images.
The backlight assembly 50 includes a mold frame 16, light emitting diodes (LEDs) 12, an LED substrate 14, a light guide plate 18, a reflective plate 20 and optical sheets 10.
The LEDs 12 emit a predetermined brightness of light corresponding to a drive signal from the LED substrate 14.
The light guide plate 18 supplies the light from the LEDs 12 to the liquid crystal display panel 4. That is, the light guide plate 18 supplies the light from its side surface to the liquid crystal display panel 4 located on its upper side.
The reflective plate 20, which is arranged in the back surface of the light guide plate 18, re-supplies the incidence light from the light guide plate 18 back toward the light guide plate 18. That is, the reflective plate 20 improves the optical efficiency by re-supplying its incident light to the light guide plate 18.
The optical sheets 10 enhance the brightness of light from the light guide plate 18 to supply the enhanced light to the liquid crystal display panel 4.
The LED substrate 14, which is connected to the first printed circuit board 24, supplies the drive signal to the LEDs 12 corresponding to control signal from the first printed circuit board.
The LED substrate 14 mounted with LEDs 12 is received and fixed, and the liquid crystal display panel 4 and backlight assembly 50 are fixed and supported, in the mold frame 16. The top chassis 2 is fixed to the upper side of the mold frame 16, and the bottom chassis 22 is fixed to the lower side of the mold frame 16. An opening is formed in the part of the bottom chassis 22 such that a light emitting display panel 30 can be inserted.
The second printed circuit board 26 is supplied with the drive signal from a drive circuit (not shown) located in the mobile phone. For this, the second printed circuit board 26 includes a mobile phone connector 28. The mobile phone connector 28 is connected to another connector attached to the drive circuit located in the mobile phone, to thus be supplied with the drive signal from the drive circuit located in the mobile phone. The second printed circuit board 26 supplied with the drive signal generates various control signals corresponding to the drive signal.
The first printed circuit board 24 is connected to the second printed circuit board 26 through a first pad unit 38 provided in the second printed circuit board 26. The first printed circuit board 24 is connected to the integrated circuit 6 of the first liquid crystal display panel 4 and LED substrate 14 by a flexible printed circuit board (not shown). The first printed circuit board 24 connected to the integrated circuit 6 and LED substrate 14 drives the integrated circuit 6 and LED substrate 14 corresponding to the control signals supplied from the second printed circuit board 26.
The light emitting display panel 30 includes a first substrate 30a and a second substrate 30b. The second substrate 30a is arranged with organic LEDs (not shown) in a matrix form. The organic LEDs generate a predetermined brightness of light corresponding to the amount of current supplied to it. The light emitting display panel 30 is connected to the second printed circuit board 26 by the second pad unit 36 of the flexible printed circuit board 32. The flexible printed circuit board 32 is mounted with an integrated circuit 34, which causes predetermined images to be displayed on the light emitting display panel 30 corresponding to the control signals from the second printed circuit board 26.
The first and second printed circuit boards 24, 26 are earthed, i.e. grounded, to the bottom chassis 22 formed of a metal material, and are thus driven stably. For this, a region on both side ends of the second printed circuit board 26 exposes its copper film to the outside, and conductive tapes 40a, 40b are attached to the copper film.
The conductive tapes 40a, 40b are connected to the bottom chassis 22 when the portable display device 60 is assembled, thus allowing the ground of the first and second printed circuit boards 24, 26 to be earthed to the bottom chassis 22. However, if the first and second printed circuit boards 24, 26 are connected to the bottom chassis 22 using the conductive tapes 40a, 40b, conductive resistance rises due to the resistance of the conductive tapes 40a, 40b. Accordingly, there exists a problem that Electrostatic Discharge (ESD) is reduced. In addition, there exists a problem that the addition of conductive tapes 40a, 40b for earthing of the first and second printed circuit boards 24, 26 raises manufacturing cost, and also increases process time.